1. Field of the Invention
This invention relates generally to the field of exercise equipment, and particularly to an apparatus for varying the amount of resistance encountered by a user during different portions of a single exercise repetition.
2. Prior Art
A great variety of machines have been developed for exercising various portions of the human body. In the majority of such machines, the user exercises against a resistance created by a suspended weight. Typically, a stack of individual weights is provided so that the user may select the amount of weight, and hence the amount of resistance, for a particular exercise.
In recent years, various electromechanical resistance systems have been proposed to replace the conventional weight stack. Such systems not only dispense with the weights, but also permit electronic control of the resistance profile during an exercise routine. As an example, U.S. Pat. No. 4,726,582 issued Feb. 23, 1988 to Fulks discloses a programmable exercise system in which conventional weights are replaced by an electric motor and a variable clutch device, such as a magnetic particle clutch. A digital processor is connected to a sensor that detects the position and direction of movement of a user operated member and controls the magnitude of the torque transmitted by the clutch. The resistive force provided to the user is thus varied as a function of the location and direction of movement of the operated member.
U.S. Pat. No. 5,020,794 issued Jun. 4, 1991 to Englehardt et al. also discloses an exercise machine in which an electric motor is used to simulate a weight stack. A computer controlled servo loop compensates for friction and inertia within the system and provides for a variable resistance profile during an exercise routine.
In a similar vein, U.S. Pat. No. 5,015,926 issued May 14, 1991 to Casler discloses an electronically controlled force application mechanism for exercise machines. This mechanism includes a constant speed high torque electric drive motor coupled to a dynamic clutch, such as a magnetic particle clutch. The torque and speed of the clutch output shaft is computer controlled to regulate the resistance profile of the exercise machine.
Prior art devices such as those discussed above that entirely eliminate suspended weights in favor of electromechanical resistance have not yet been developed to the point where they give the user the same "feel" as a conventional weight machine. Nevertheless, electromechanical resistance systems are extremely versatile in terms of customizing and/or varying resistance profiles.